Stress optimization in DC magnetron sputtered AlN layers for fully clamped bistable piezoelectric plate devices

In this paper, we demonstrate the fabrication and characterization of bistable piezoelectric plates with a precisely tuned residual stress to achieve buckling-induced bistability. The plate consist of a multilayered structure, with a piezoelectric aluminum nitride layer sandwiched between top and bottom electrode layers. The stress in the aluminum nitride thin film is tuned by adjusting the DC magnetron sputtering parameters, including sputtering pressure, gas flow rates, target-substrate distance, and substrate bias voltage to introduce the compressive stress needed to induce plate buckling. Experimental results demonstrate that reducing sputtering pressure while controlling nitrogen flow, with no argon admixture, and applying a substrate bias voltage above 10 V enables compressive stress in the aluminum nitride layer within the desired range of -800 to -600 MPa, resulting in bistable plates. The bistability of the fabricated plates is evaluated by analyzing their potential energy profiles under applied external perpendicular forces, using a bulge test setup, where uniform air pressure is applied to the plate surface. The plates exhibit a characteristic hysteresis loop in their load–deflection response, with transitions between buckled-down and buckled-up states at approximately 10 mbar and -30 mbar, respectively. The initial buckling amplitude of the fabricated plates, within the optimized stress range, is measured to be 5-7 μ m, with a total displacement of 10-12 μ m when switching between both states. Furthermore, in each stable state, the plates exhibit an additional displacement of approximately 5 μ m when subjected to a relative air pressure of ∼ 1 bar. • Stress tuning in AlN layers enables bistability in piezoelectric plates. • Compressive stress in AlN induced via sputtering parameter control. • Experimental load–deflection reveals bistability with buckling amplitudes of ∼ 7 μ m. • Residual stress and asymmetry estimated from experimental potential energy profile.